fix to pass doctest
fix to pass doctest

keisuke-umezawa/chainer,keisuke-umezawa/chainer,hvy/chainer,keisuke-umezawa/chainer,rezoo/chainer,wkentaro/chainer,niboshi/chainer,wkentaro/chainer,tkerola/chainer,pfnet/chainer,chainer/chainer,niboshi/chainer,chainer/chainer,jnishi/chainer,ktnyt/chainer,niboshi/chainer,ktnyt/chainer,okuta/chainer,wkentaro/chainer,ktnyt/chainer,chainer/chainer,ronekko/chainer,okuta/chainer,hvy/chainer,keisuke-umezawa/chainer,hvy/chainer,hvy/chainer,anaruse/chainer,aonotas/chainer,niboshi/chainer,wkentaro/chainer,jnishi/chainer,okuta/chainer,jnishi/chainer,jnishi/chainer,chainer/chainer,okuta/chainer,ktnyt/chainer